Primary immunisation and febrile convulsions in Oxford 1972-5.

A three-year study of febrile convulsions in Oxford with comprehensive notification from general practice and hospitals showed a 3% risk for all children of suffering at least one febrile convulsion by the age of 5 years. Children were most at risk between 6 and 27 months, and febrile convulsions were most likely to be prolonged in children aged 9-15 months. The association between febrile convulsions and primary immunisations in the preceding 28 days was compared in case and control children, matched for age and sex. Results suggested that such association was a chance relationship with age. If association was direct, the febrile convulsion rates per 1000 immunisation doses were estimated as follows: diphtheria, pertussis, tetanus--0-09 per 1000; poliomyelitis--0-6 per 1000; and measles--0-9 per 1000. Hence if any of these vaccines had a secific causal relationship with febrile convulsions, these rates would probably have been much higher.